1. Field of the Invention
The present invention relates to a photocatalyst having a visible light activity, to a method for producing the photocatalyst, a method of photodecomposition using a light involving visible rays, and to a device using the photocatalyst.
2. Background Art
Various studies on deodorization and sterilization using photocatalysts have been made to present, and some of them have been put to practice. For instance, in WO94/11092 is disclosed a method for treating air using a photocatalyst under the irradiation of room light. In Japanese Patent Laid-Open No. 102678/1995 is disclosed a method for preventing medical infection from occurring in hospitals by using photocatalysts. In both cases, an oxide semiconductor such as titanium dioxide and the like is used as the photocatalyst, which requires an ultraviolet radiation 400 nm or shorter in wavelength for the excitation.
However, sunlight or an artificial light source used as the excitation light source also includes visible rays in addition to ultraviolet radiations. Yet, the visible rays are not used in the photocatalysts comprising oxide semiconductors such as titanium dioxide as described above; hence, such photocatalysts are extremely in efficient as viewed from the point of energy conversion efficiency.
It is well known that titanium dioxide acquires photocatalytic activity by injecting metallic ions such as chromium by using ion implantation method. However, this method is practically unfeasible because it involves the use of voluminous equipment.
On the other hand, it is reported that the catalytic activity of titanium dioxide under ultraviolet radiation can be increased by providing it with TiC coating using plasma CVD (see Japanese Patent Laid-Open No. 87857/1997). However, the literature does not teach any photocatalytic activity under the irradiation of visible light.
In the light of such circumstances, an object of the present invention is to provide a novel photocatalyst capable of using visible light.
A second object of the present invention is to provide a production method for the photocatalyst above.
Furthermore, a third object of the present invention is to provide a method for removing various types of substances including organic matter or bacteria by photode composition using the novel photocatalyst described above.
Further, a fourth object of the present invention is to provide a device using the novel photocatalyst above.